DESCRIPTION: The purpose of this R21 is to characterize the molecular events in fungal biofilm formation from the initial attachment of C. albicans to an abiotic surface through the development of a mature and continuous cellular network that is firmly adherent to that surface. It is our hypothesis that transcription profiling during the development of a C. albicans biofilm will result in the identification of key stages, pathways and functions that are expressed during this process. The process of biofilm formation in both bacteria and fungi has primarily been assessed through the description of events, at the microscopic and macroscopic level, which result in the establishment of biofilms on inert surfaces. In the case of fungal biofilms, little is known about the underlying molecular process associated with biofilm development. With the exception of limited biochemical characterization of the extracellular matrix, the changes in drug susceptibility in cells in biofilms and the effects of various mutations associated primarily with the regulation of hyphal morphogenesis, little is known about the molecular changes which may be manifest in adherent cells as compared with planktonic cells. Less is known about the molecular changes, which may occur in adherent cells as these proceed to establish highly-structured cellular networks. In this era of high throughput genome profiling, we have the unique ability to address this emerging problem by using methods that allow comprehensive analysis of the changes in gene expression during the course of biofilm development. For this study, we will use DNA microarrays, which we have developed with Dr. Ronald Davis and colleagues at the Stanford Genome Technology Center (STGC); these arrays are inclusive of the entire genome of C. albicans. RNA samples will be isolated from adherent and planktonic cells in a highly-controlled time course which will span the 24h period required for biofilm formation under the conditions described in the application. The large data set that will emerge from such a study will be carefully analyzed using a variety of algorithms that will allow definition of changes in specific genes and in gene clusters/pathways, which may be expressed during the course of biofilm development. By comparing gene expression in adherent and non-adherent cells, we will learn whether and to what degree, attachment to an inert surface can affect gene expression.